1. Field of the Invention
The present invention relates to an encoder, and, more particularly, to an encoder in which interference beam is formed by a plurality of diffracted beams generated in a diffraction grating, and the displacement of the above-described diffraction grating is measured by converting the thus formed interference beam into a signal.
2. Related Background Art
Hitherto, encoders of the type described above exhibit excellent resolving power with respect to conventional photoelectric encoders using main scales in which a multiplicity of slits are arranged and index scales in which a plurality of slits are formed. In order to improve the resolving power of the encoder of the type described above, a signal obtained from the interference beam is usually electrically divided so that a multiplicity of pulses are formed in the manner similar to the operation of the conventional photoelectric encoder.
However, the above-described method in which the signal is electrically divided suffers from a unsatisfactory precision. Therefore, an encoder in which a signal exhibiting further improved resolving power (that is, a signal including a multiplicity of pulses) can be directly obtained from the interference beam has been required.
To this end, the applicant of the present invention has disclosed, in U.S. Ser. No. 190,247, an encoder capable of forming an interference beam from the diffracted beams which have been diffracted three times or more in the diffraction grating thereof.